What do you look for in a partner? Surely that depends on what the partner is for – you’d probably want a business partner to be innovative, a choir buddy to be musical and a romantic partner to be attractive and funny. But how do such qualities and skills compare with simply being decent, as in fair and generous?
Humans are unusually prosocial – we routinely cooperate with non-relatives to an extent that far surpasses that of any other living creature. Nevertheless, there is a significant downside to helping others: the risk of being suckered by a cheating individual – someone who takes the benefits of cooperation without contributing to the pot. Understanding how humans form mutually productive relationships, while at the same time avoiding social parasites, is the key to understanding the evolution of extreme sociality in humans.
To find out, we recruited 788 participants from an online crowdsourcing website to take part in an online, modified version of a classic anthropological experiment: the dictator game. This is a simple economic task used to gauge prosocial tendency. Individuals interact in pairs as “dictators” and “receivers”. Dictators are given some money and told that they can give as much (or as little) as they like to receivers. Receivers have no control over the allocation and must accept any offer the dictator makes.
Our dictator game was modified in a few important ways, to allow us to determine how people trade off ability versus willingness to give when choosing partners. First, we gave rich dictators five times as much money to share with receivers compared to their poorer counterparts, meaning rich ones could offer higher absolute payoffs – even when relatively stingy. We also modified wealth stability. In stable environments, the rich stayed rich and the poor stayed poor, whereas in unstable environments, current wealth was not predictive of wealth in the next game.
Finally, receivers could choose or avoid dictators on the basis of their reputation for having been fair or stingy in the previous game. Receivers observed the decisions made by two different dictators in a first game – and then decided which of these individuals they would like to choose as their own partner in a second game. We were especially interested in how receivers prioritised wealth over fairness in a partner when these traits were opposed to one another.
The results, published in Royal Society Open Science, were striking. As expected, when wealth and fairness were aligned (for example, when choosing between rich-fair and poor-fair partners), receivers typically picked the rich partner – and this preference was especially pronounced in stable environments. When choosing between rich-stingy and poor-fair partners, however, the majority of receivers preferred the poorer partner – even in stable environments where the poor tended to stay poor (57% did this). This was despite the fact that they had an expected payoff reduction of almost 25%. As expected, receivers showed an even stronger preference for poor-fair over rich-stingy dictators in unstable environments, with over 85% choosing the poorer partner.
Generosity in the real world
The decision rules we use to select partners might not be economically rational, but they are probably ecologically rational, in that they somehow increase fitness in the environment that they were selected in.
But is there evidence that humans actually operate like this in the real world? Some evidence from hunter-gatherer societies has shown that generosity is indeed more important than hunting skills in determining the popularity of hunters within their social networks. The best hunters may catch more meat, but it is those who share what they catch who are preferred as hunting partners. Our study supports these findings: ability to give is valuable, but willingness to give is indispensable.
And could it hold true for romantic relationships? It’s hard to do the exact same experiment with the most common things we look for in a partner – such as intelligence, humour and good looks – as these tend to be much more stable traits than wealth. But, in the experiment, the majority of people picked poor-fair partners over rich-stingy even when wealth was unchangeable. So there may be a similar pattern in dating where generosity or fairness could trump looks or intelligence. Future work could explore the relative importance of these traits when it comes to dating.